Having determined the crystal structure of deoxy HbS at 5A resolution, it is proposed to extend the resolution to 3A in order to determine in more detail how Val beta 6 B3 participates in intermolecular bonding. It is proposed to co-crystallize deoxy Hb S with Hb C, with which it interacts, in order to get another view of interaction between mutant hemoglobin molecules. The crystal structure of such mixed crystals would be determined as before, by means of translation and rotation searches.